首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3770篇
  免费   263篇
  国内免费   4篇
电工技术   44篇
综合类   5篇
化学工业   884篇
金属工艺   72篇
机械仪表   55篇
建筑科学   164篇
矿业工程   5篇
能源动力   142篇
轻工业   264篇
水利工程   33篇
石油天然气   15篇
无线电   295篇
一般工业技术   791篇
冶金工业   610篇
原子能技术   26篇
自动化技术   632篇
  2023年   60篇
  2022年   98篇
  2021年   169篇
  2020年   116篇
  2019年   114篇
  2018年   140篇
  2017年   128篇
  2016年   138篇
  2015年   116篇
  2014年   186篇
  2013年   261篇
  2012年   228篇
  2011年   291篇
  2010年   194篇
  2009年   179篇
  2008年   187篇
  2007年   169篇
  2006年   148篇
  2005年   94篇
  2004年   107篇
  2003年   69篇
  2002年   78篇
  2001年   32篇
  2000年   26篇
  1999年   44篇
  1998年   63篇
  1997年   46篇
  1996年   28篇
  1995年   34篇
  1994年   26篇
  1993年   24篇
  1992年   17篇
  1990年   19篇
  1989年   17篇
  1988年   12篇
  1987年   12篇
  1985年   23篇
  1984年   19篇
  1983年   17篇
  1982年   22篇
  1981年   26篇
  1980年   13篇
  1979年   25篇
  1978年   19篇
  1977年   17篇
  1976年   23篇
  1975年   18篇
  1974年   18篇
  1972年   11篇
  1971年   12篇
排序方式: 共有4037条查询结果,搜索用时 15 毫秒
71.
72.
Two proprietary biocides were compounded and extruded at three concentrations, respectively, into high density polyethylene-maple wood flour lumber (HDPE-MWL) and evaluated for their efficacy to control fungal colonization and discoloration using the ASTM Standard G 21-96. Although the silver biocide used in this study did not control fungal colonization and discoloration of HDPE-MWL, statistically significant difference was observed between the highest silver biocide concentration and those of the two lower silver biocide concentrations. The latter exhibited no significant difference with the controls. In contrast, the three levels of zinc biocides showed significant difference from each other with respect to their efficacy against fungal colonization and discoloration of HDPE-MWL. Overall, only the zinc biocide was efficacious against fungal colonization and discoloration. The biocide containing zinc as an active biocidal agent was most efficacious at 1% (by weight) concentration.  相似文献   
73.
Cytochrome p450 1A (CYP1A) gene expression in fish liver increases upon exposure to a variety of chemical compounds, including organochlorine compounds (OCs) and polycyclic aromatic hydrocarbons (PAHs). To use this physiological response as a marker of environmental impact, we developed and validated a set of primers to quantify CYP1A expression by qRT-PCR in the brown trout, Salmo trutta. These primers were used to explore the natural variability of CYP1A expression in 8 isolated populations (65 samples) from European remote lakes, in a geographical distribution encompassing the Tyrolean Alps, Pyrenees, Rila, Tatras, and Norwegian and Scottish mountains. CYP1A expression values varied more than 2 orders of magnitude among samples, with strong variations within each population. CYP1A expression values were significantly elevated in Tatras and Pyrenees fish populations, whereas the lowest median values were found in populations from the Tyrolean Alps and Rila. These values correlated with the content of different environmentally relevant pollutants in the sediments of the lakes harboring each fish population, particularly with HCB and 4,4'-DDE contents. To our knowledge, this works represents a first report of a physiological response linked to persistent organic pollutants in fish from mountain lakes.  相似文献   
74.
引言 如果你的公司设计、生产或销售抗菌织物.那么你首先要知道这些产品能带给顾客的特性。你不得不花费时间和精力去了解抗茵的知识.并且在这个过程中极有可能获得大量的有关微生物和实验室测试的知识。毫无疑问.你也会感谢这些高性能织物带来的商业潜力。  相似文献   
75.
76.
77.
In this study, the relationship between sensory evaluation and several objective metrics of beef tenderness was tested. Objective metrics included shear force, sarcomere length, collagen content, myofibrillar, and sarcoplasmic protein solubility and particle size analysis. These results were compared to consumer panel scores of tenderness for the same aged beef striploin (longissimus lumborum muscle) samples. There was found to be a significant relationship between sarcomere length, shear force, and particle size with tenderness scores. Collagen content and protein solubilities were not associated to tenderness scores (p > 0.05). Sarcomere length contributions for explaining tenderness variation were overlapped by the contributions of shear force (collinearity). Independent models demonstrated that the lower 95% confidence interval of the fitted regression line exceeded 50% acceptance of tenderness when shear force values <42.6 N and when particle size values <198 μm. We can recommend these as thresholds for consumer acceptance of beef tenderness, although considerations of sample type, analytical methodology, and consumer demographics should be made prior to their adoption. This provision was based on the variation in tenderness scores evident between individual panelists and experimental striploins.  相似文献   
78.
Enriching the micronutrients, selenium (Se) and lithium (Li), in grapes to improve their nutraceutical properties were implemented by foliar application of organic fertiliser rich in Se and Li onto five grape cultivars. The effects of this biofortification on vine vigour, fruit quality, overall micronutrients and phenolic compounds also were investigated. Agronomic biofortification was found greatly increased the Se and Li content in the whole grape by multiple times, meanwhile it did not significantly affect the vine vigour and fruit quality of grapes. However, the biofortification did impact the Ionome (including all the mineral nutrients and trace elements) and phenolic compounds in grapes and this varied among cultivars. This study demonstrated foliar spray of organic Se/Li fertiliser was a very effective strategy to biofortify these micronutrients in grape berries, particularly in the skin, and therefore might be a promising strategy to increase the consumption and awareness of these grapes.  相似文献   
79.
Beardless barb is a common fish species used in fermentation of fish paste Ka-pi-plaa. Autolytic profile of beardless barb muscle showed the maximum autolysis was at 50 °C, at both acidic and alkaline pH values. With augmentation concentration of NaCl, autolytic activity slightly decreased. Endogenous proteinases isolated from fish muscle in crude extract forms were also characterised. The acidic proteinases had optimum activity at pH 3.0 and 50°C, and they showed higher proteolytic activity than the alkaline proteinases which were optimally active at pH 9.0 and 50 °C. Proteinases in peak at pH 3.0 were inhibited by pepstatin A, but those in peak at pH 9.0 were highly inhibited by PMSF, TLCK and soybean trypsin inhibitor, suggesting that both aspartic and serine proteinases were existed in beardless barb muscle. The proteinases were stable in pH range of 2.0-5.0 but unstable at the temperatures higher than 40 °C. NaCl suppressed the proteolytic activity, ATP activated the proteinase activity, while CaCl2, MgCl2 and CoCl2 exhibited no influence on the activity. The results implied that cathepsin D is the predominant proteinase responsible for autolysis in beardless barb. The findings were useful to improve the processing and qualities of Ka-pi-plaa product using beardless barb as raw material.  相似文献   
80.
The melting behaviour of heterogeneously chlorinated and sulphonated high-density polyethylene was studied by differential scanning calorimetry. It was found that an increase in Tm takes place at high degrees of substitution in the amorphous phase. For sulphonated polyethylenes the increase in Tm was also dependent on the type of the counterion. The effect is interpreted as a decrease in configurational entropy upon fusion due to the restraints that the highly chlorinated and sulphonated amorphous regions impose on the adjacent crystallites.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号